from onewire import OneWire

class DS18X20(object):
  def __init__(self, pin):
    self.ow = OneWire(pin)
    # Scan the 1-wire devices, but only keep those which have the
    # correct # first byte in their rom for a DS18x20 device.
    self.roms = [rom for rom in self.ow.scan() if rom[0] == 0x10 or rom[0] == 0x28]

  def read_temp(self, rom=None):
    """
    Read and return the temperature of one DS18x20 device.
    Pass the 8-byte bytes object with the ROM of the specific device you want to read.
    If only one DS18x20 device is attached to the bus you may omit the rom parameter.
    """
    rom = rom or self.roms[0]
    ow = self.ow
    ow.reset()
    ow.select_rom(rom)
    ow.write_byte(0x44)  # Convert Temp
    while True:
      if ow.read_bit():
        break
    ow.reset()
    ow.select_rom(rom)
    ow.write_byte(0xbe)  # Read scratch
    data = ow.read_bytes(9)
    return self.convert_temp(rom[0], data)

  def read_temps(self):
    """
    Read and return the temperatures of all attached DS18x20 devices.
    """
    temps = []
    for rom in self.roms:
      temps.append(self.read_temp(rom))
    return temps

  def convert_temp(self, rom0, data):
    """
    Convert the raw temperature data into degrees celsius and return as a float.
    """
    temp_lsb = data[0]
    temp_msb = data[1]
    if rom0 == 0x10:
      if temp_msb != 0:
      # convert negative number
        temp_read = temp_lsb >> 1 | 0x80  # truncate bit 0 by shifting, fill high bit with 1.
        temp_read = -((~temp_read + 1) & 0xff) # now convert from two's complement
      else:
        temp_read = temp_lsb >> 1  # truncate bit 0 by shifting
      count_remain = data[6]
      count_per_c = data[7]
      temp = temp_read - 0.25 + (count_per_c - count_remain) / count_per_c
      return temp
    elif rom0 == 0x28:
      return (temp_msb << 8 | temp_lsb) / 16
    else:
      assert False
